In Reply The results of our trial showed a statistically significant reduction in the level of incident myopia and a moderate reduction on overall change in spherical equivalent refraction, but no effect on progression. However, it should be noted that the prevalence of myopia in the study sample was low at baseline, and thus an analysis of progression does not have great statistical power.

Drs Pan and Liu suggest that time outdoors does not affect progression, and that other strategies will be needed to control progression. We did not find effects on progression, which is consistent with most of the evidence from longitudinal studies and another clinical trial from Taiwan.1 However, there is conflicting evidence2 and evidence of seasonal effects, which suggest that progression rates can be regulated by environmental factors.